1. Field of the Invention
The present invention relates to an estimation apparatus and method for a cylinder intake air amount of an internal combustion engine including a supercharger.
2. Description of the Related Art
A control system for an engine including a supercharger has been known in the related art in order to increase an output of an internal combustion engine (hereinafter also referred to as “engine”). As an example of the supercharger, there is known a turbocharger (hereinafter also referred to as “T/C”) in which a compressor driven by rotating a turbine at a high speed by an energy provided by an exhaust gas is installed in an intake system of the engine.
Moreover, as another example of the supercharger, there is known a mechanical supercharger (hereinafter also referred to as “S/C”) in which a compressor driven by a crankshaft via a belt or the like is installed in the intake system of the engine. Moreover, in recent years, there are known a supercharger in which a plurality of T/Cs are connected in parallel or serial, a supercharger including both a T/C and an S/C, and an electric charger in which a compressor is directly driven by a motor.
Moreover, as a method of acquiring an intake air amount in the engine control system, there are known a method (hereinafter referred to as “AFS method”) of detecting the intake air amount by using an airflow sensor (hereinafter referred to as “AFS”) and a so-called speed density method (hereinafter referred to as “S/D method”) of estimating the intake air amount based on a pressure in an intake manifold. It should be noted that both the AFS method and the S/D method are used in the control system for an engine including a supercharger.
On this occasion, the method of estimating the intake air amount by the S/D method estimates an intake air amount (hereinafter referred to as “cylinder intake air amount”) actually entering the cylinder from the intake manifold pressure based on a correlation between the intake manifold pressure and the intake air amount adapted in advance, and the cylinder intake air amount can be estimated by approximately the same method both in the engine control system for an engine including a supercharger and in the engine control system for an engine without a supercharger (hereinafter referred to as “N/A system”).
Moreover, this method directly reflects a change in intake manifold pressure to an estimated value of the cylinder intake air amount, resulting in an excellent response characteristic during a transient operation. On the other hand, this method has such a problem that an estimation error in the cylinder intake air amount during operations including a steady state operation is relatively large due to an error caused by a machine difference from an engine used for the adaptation and an error caused by a difference in environment from that during the adaptation.
In contrast, the method of detecting the intake air amount by the AFS method directly measures the airflow rate (hereinafter referred to as “AFS intake air amount”) passing through an AFS installed part (hereinafter referred to as “AFS part”). Moreover, the cylinder intake air amount during the steady state operation is approximately the same as the AFS intake air amount, and it is considered that a calculation error of the cylinder intake air amount during the steady state operation is relatively small.
On this occasion, a distance from the AFS part to the cylinder is long, and the cylinder intake air amount needs to be calculated by simulating a response lag due to the distance. It is thus considered that a calculation precision of the cylinder intake air amount during a transient operation depends on a precision of a physical model of the intake system simulating the response lag. Thus, physical models (for example, refer to Japanese Patent No. 5328967) modeling a response lag in the intake system for causing the air that has passed through the throttle valve to enter the cylinder have been proposed.
However, the related art has the following problem.
The physical model of the intake system for the N/A system is detailed in Japanese Patent No. 5328967, but no reference is made about a control system for an engine including a supercharger.
Even if the physical model described in Japanese Patent No. 5328967 is directly applied to the control system for an engine including a turbocharger, only the response lag in a throttle downstream portion can be simulated. The model does not consider a throttle upstream portion extending from the AFS part to the compressor, and thus there is a problem in that a large error is generated in a response characteristic during the transient operation.